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It is a text based script lanugage or programing language that creates plateform for both the client and server side to created fully futured website element
Git and GitHub solves the problem of losting cods that you have done previosly so that to traceback easly
When you fork repository you change it from remote to local or to your GitHub account.
if You clone repository it will copy to your issue.
Pull request is a process of merging from your branch to the organization branch